Lateral high electron mobility transistor with Schottky junction

ABSTRACT

A lateral HEMT includes a first semiconductor layer on a second semiconductor layer, a heterojunction at an interface between the first semiconductor layer and the second semiconductor layer, and a rectifying Schottky junction. The rectifying Schottky junction has a first terminal electrically coupled to a source electrode and a second terminal electrically coupled to the second semiconductor layer.

PRIORITY CLAIM

This application is a Continuation of U.S. application Ser. No.13/090,350, filed on 20 Apr. 2011, the content of said applicationincorporated herein by reference in its entirety.

BACKGROUND

For semiconductor devices, for example power semiconductor devices,compound semiconductors such as III-V compound semiconductors havebecome more and more important in recent years, since they allow forsemiconductor devices with higher doping and shorter drift zone comparedto silicon-based semiconductor devices while retaining a high blockingcapability.

Up to now, power semiconductor devices based on III-V compoundsemiconductors are realized as lateral devices. These devices are knownas high electron mobility transistors (HEMTs). An HEMT includes severallayers of differently doped semiconductor materials with different bandgaps. Due to the different band gaps of the individual layers, atwo-dimensional electron gas (2DEG) is formed at the interface of theselayers, the two-dimensional electron gas serving as a conductivechannel. The mobility of the electrons as well as the 2D-electron chargecarrier density is very high in the two-dimensional electron gas.

The two-dimensional electron gas is provided in a region between asource electrode and a drain electrode. When the HEMT is used as aswitch, e.g., as a switch for inductive loads, various operation modessuch as turn-off of inductive loads come up. An HEMT that meets demandson a switch operating in various modes is desirable.

SUMMARY

According to an embodiment of a lateral HEMT, the lateral HEMT includesa substrate, a first semiconductor layer above the substrate and asecond semiconductor layer on the first semiconductor layer. The lateralHEMT further includes a gate electrode, a source electrode, a drainelectrode and a rectifying Schottky junction. A first terminal of therectifying Schottky junction is electrically coupled to the sourceelectrode and a second terminal of the rectifying Schottky junction iselectrically coupled to the second semiconductor layer.

According to a further embodiment of a lateral HEMT, the lateral HEMTincludes a substrate, a first semiconductor layer above the substrateand a second semiconductor layer on the first semiconductor layer. Thelateral HEMT further includes a gate electrode, a source electrode, adrain electrode and a Schottky junction. The Schottky junction includesa Schottky contact metal on the second semiconductor layer. The Schottkycontact metal is electrically coupled to the source electrode. Ashortest lateral distance between the gate electrode and the drainelectrode is larger than the shortest lateral distance between theSchottky junction and the drain electrode.

According to another embodiment of a lateral HEMT, the lateral HEMTincludes a substrate, a first semiconductor layer above the substrateand a second semiconductor layer on the first semiconductor layer. Thelateral HEMT further includes a gate electrode, a source electrode, adrain electrode and a rectifying Schottky junction. A first terminal ofthe rectifying Schottky junction is electrically coupled to the sourceelectrode and a second terminal of the rectifying Schottky junction iselectrically coupled to the second semiconductor layer. The lateral HEMTfurther includes a passivation layer above the second semiconductorlayer, a drift region having a lateral width w_(d), and at least onefield plate. The at least one field plate is arranged at least partiallyon the passivation layer in a region of the drift region and has alateral width w_(f), wherein w_(f)<w_(d).

Those skilled in the art will recognize additional features andadvantages upon reading the following detailed description, and uponviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the present invention and are incorporated in andconstitute a part of this specification. The drawings illustrateembodiments of the present invention and together with the descriptionserve to explain principles of the invention. Other embodiments of thepresent invention and many of the intended advantages of the presentinvention will be readily appreciated as they become better understoodby reference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference numerals designate corresponding similar parts. The featuresof the various illustrated embodiments can be combined unless theyexclude each other.

Embodiments are depicted in the drawings and are detailed in thedescription which follows.

FIG. 1 illustrates a diagrammatic cross-section through a section of alateral HEMT including a rectifying junction according to an embodiment.

FIG. 2 illustrates a diagrammatic plan view of a section of the lateralHEMT illustrated in FIG. 1.

FIG. 3A illustrates a diagrammatic cross-section through a section of alateral HEMT including a rectifying junction and a field plate accordingto an embodiment.

FIG. 3B illustrates a diagrammatic cross-section through another sectionof the lateral HEMT illustrated in FIG. 3A.

FIG. 4 illustrates a diagrammatic plan view of a section of the lateralHEMT illustrated in FIGS. 3A and 3B.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the invention maybe practiced. In this regard, directional terminology, such as “top”,“bottom”, “front”, “back”, “leading”, “trailing”, etc., is used withreference to the orientation of the figure(s) being described. Becausecomponents of the embodiments can be positioned in a number of differentorientations, the directional terminology is used for purposes ofillustration and is in no way limiting. It is to be understood thatother embodiments may be utilized and structural or logical changes maybe made without departing from the scope of the present invention. Thefollowing detailed description, thereof, is not to be taken in alimiting sense, and the scope of the present invention is defined by theappended claims.

A number of embodiments will be explained below. In this case, identicalstructural features are identified by identical or similar referencesymbols in the figures. In the context of the present description,“lateral” or “lateral direction” should be understood to mean adirection or extent that runs generally parallel to the lateral extentof a semiconductor material or carrier. The lateral direction thusextends generally parallel to these surfaces or sides. In contrastthereto, the term “vertical” or “vertical direction” is understood tomean a direction that runs generally perpendicular to these surfaces orsides and thus to the lateral direction. The vertical directiontherefore runs in the thickness direction of the semiconductor materialor carrier.

As employed in this specification, the terms “coupled” and/or“electrically coupled” are not meant to mean that the elements must bedirectly coupled together—intervening elements may be provided betweenthe “coupled” or “electrically coupled” elements.

Spatially relative terms such as “under”, “below”, “lower”, “over”,“above”, “upper” and the like are used for ease of description toexplain the positioning of one element relative to a second element.These terms are intended to encompass different orientations of thedevice in addition to different orientations than those depicted in thefigures.

Further, terms such as “first”, “second”, and the like, are also used todescribe various elements, regions, sections, etc. and are also notintended to be limiting. Like terms refer to like elements throughoutthe description.

As used herein, the terms “having”, “containing”, “including”,“comprising” and the like are open ended terms that indicate thepresence of stated elements or features, but do not preclude additionalelements or features. The articles “a”, “an” and “the” are intended toinclude the plural as well as the singular, unless the context clearlyindicates otherwise.

It is to be understood that the features of the various embodimentsdescribed herein may be combined with each other, unless specificallynoted otherwise.

FIG. 1 illustrates a diagrammatic cross-section through a section of alateral HEMT 100 according to an embodiment. In this embodiment, thelateral HEMT 100 includes a substrate 122 and a buffer layer 121arranged on the substrate 122. The substrate 122 may include Si, SiC,GaN or Al₂O₃. The buffer layer 121 may include AlN, GaN or AlGaN.

In some embodiments, the buffer layer 121 includes a plurality ofindividual layers, and each of the individual layers may include AlN,GaN or AlGaN. Depending on the requirements of the lateral HEMT 100, asuitable buffer layer 121 may therefore be provided.

According to other embodiments, the substrate 122 or the combination ofthe substrate 122 and the buffer layer 121 may be a metal carrier suchas a Cu carrier. A thickness of the metal carrier may be appropriatelychosen to provide mechanical stability to the layer stack arrangedthereon. In addition, the metal carrier supports dissipation of heatgenerated in the device arranged thereon in an operation mode of thedevice. As an example, the thickness of a metal carrier made of Cu maybe between 15 μm to 50 μm, in particular between 30 μm to 40 μm.Omitting the buffer layer 121 may improve heat dissipation since thisbuffer layer which supports growth of GaN layers on initial siliconsubstrates may decrease heat dissipation due to a high thermal boundaryresistance. The metal carrier may be formed by first removing atransitional carrier such as a carrier made of Si, SiC or Al₂O₃, e.g.,by grinding or etching. Removal of the transitional carrier may bepurely mechanical with a stop on a buffer layer or may start with amechanical removal process followed by an etching process. Then, thebuffer layer 121 is removed, e.g., by plasma etching, and a seed layerand/or ohmic contact layer, e.g., a single layer or layer stack isformed followed by a thickening with a metal and/or a metal alloy to endup with the metal carrier. During the formation of the metal carrier ata rear side of the work piece, i.e., chip in process, the work piece maybe mechanically fixed to another carrier via a front side.

In the embodiment illustrated in FIG. 1, a first semiconductor layer 111is arranged on the buffer layer 121. A second semiconductor layer 112 isat least partially arranged on the first semiconductor layer 111. In theillustrated embodiment, the first semiconductor layer 111 includeslightly n-doped GaN, which is typically depleted by fixed charges at theinterface or which is lightly n-conducting and contains deep traps toreduce the concentration of free charge carriers and the secondsemiconductor layer 112 includes AlGaN. The AlGaN of the secondsemiconductor layer 112 is typically compensated, i.e., it has no freecharge carriers and is therefore electrically insulating. At theinterface between the first semiconductor layer 111 and the secondsemiconductor layer 112, which form a heterojunction, a two-dimensionalelectron gas (2DEG) is formed, which is schematically illustrated inFIG. 1 by a dashed line 124.

The lateral HEMT 100 further includes a source electrode 116, a drainelectrode 117 and a gate electrode 118. In the illustrated embodiment,the source electrode 116 and the drain electrode 117 are each arrangedon the first semiconductor layer 111. In other embodiments, the sourceelectrode 116 and the drain electrode 117 are each arranged on thesecond semiconductor layer 112 and the two-dimensional electron gas iselectrically contacted by alloying the source electrode 116 and thedrain electrode 117 into the second semiconductor layer 112. The sourceelectrode 116 and the drain electrode 117 electrically contact the firstsemiconductor layer 111, the second semiconductor layer 112 and thetwo-dimensional electron gas.

Between the source electrode 116 and the drain electrode 117, a driftregion 114 is provided in the region of the two-dimensional electrongas. The gate electrode 118 is arranged on the second semiconductorlayer 112 in a region between the source electrode 116 and the drainelectrode 117 or in some embodiments may be at least partially recessedinto the second semiconductor layer 112 for normally-off devices.

A passivation layer 113 is arranged on the second layer 112 and at leastpartially surrounds the gate electrode 118. By way of example, thepassivation layer 113 may include a material selected from the group ofSi_(x)N_(y), SiO₂ and Al₂O₃.

The gate electrode 118 is configured to control the conductivity betweenthe source electrode 116 and the drain electrode 117 of the lateral HEMT100 by a suitable voltage applied to the gate electrode 118. The sourceelectrode 116, the drain electrode 117 and the gate electrode 118include an electrically conductive material, for example a metal orhighly doped polysilicon.

The lateral HEMT 100 further includes a rectifying junction. In theillustrated embodiment, the rectifying junction is a Schottky junction131 including the second semiconductor layer 112 and a Schottky contactmetal 132 on the second semiconductor layer 112. By way of example, theSchottky contact metal 132 may include at least one of Ni, Pt, W, Mo,TiSi₂, WSi₂, CoSi₂. Formation of the Schottky junction 131 may includeion implantation, e.g., CF₄ plasma ion implantation, before formation ofthe Schottky contact metal 132. According to yet another embodiment, therectifying junction of the lateral HEMT 100 includes a semiconductorband discontinuity induced by semiconductor materials on the secondsemiconductor layer 112 that have a work function different from thework function of the material of the second semiconductor layer 112.

The Schottky contact metal 132 is electrically coupled to the sourceelectrode 116 via a trough contact 119 and a wiring 115. The wiring 115is arranged at least partially on the passivation layer 113 in a regionof the drift region 114. The wiring 115 includes an electricallyconductive material such as a metal or highly doped polysilicon. By wayof example, the wiring 115 may be a part of a patterned metal layer ormetal alloy layer such as a layer or layer stack including Al, AlSi,AlTi, AlCu, AlSiTi, AlSiCu, Cu.

The through contact 119 is arranged between the wiring 115 and theSchottky contact metal 132 in a region of the passivation layer 113 anddirectly contacts both the wiring 115 and the Schottky contact metal132. The through contact 119 includes an electrically conductivematerial, for example a metal or highly doped polysilicon.

The gate electrode 118 is electrically coupled to a gate supply in aregion other than the region illustrated in the diagrammaticcross-section of FIG. 1. By way of example, the gate electrode 118 maybe electrically coupled to the gate supply in a peripheral region of thelateral HEMT 100, e.g., outside of the drift region 114. By way ofexample, the gate electrode 118 may be electrically coupled to the gatesupply via a through contact and a wiring formed which may be processedtogether with the through contact 119 and the wiring 115, respectively.

A shortest lateral distance between the gate electrode 118 and the drainelectrode 117 is denoted as d₁. A shortest lateral distance between therectifying junction, i.e., the Schottky contact metal 132, and the drainelectrode 117 is denoted as d₂. In the embodiment illustrated in FIG. 1,the shortest lateral distance d₁ between the gate electrode 118 and thedrain electrode 117 is larger than the shortest lateral distance d₂between the rectifying junction and the drain electrode 117, i.e., arelation d₁>d₂ holds.

In the embodiment illustrated in FIG. 1, the gate electrode 118 and theSchottky contact metal 132 of the rectifying junction are separate partsof a same patterned metal layer. Apart from the gate electrode 118 andthe Schottky contact metal 132, other parts of this same pattered metallayer may be present in regions different from the region illustrated inthe diagrammatic cross-section of FIG. 1. The metal layer may bepatterned by lithography, e.g., by deposition of a resin, followed byexposure of the resin via a mask, development of the exposed resin, andetching of the resin to transfer a pattern of the mask into the metallayer.

The rectifying junction of the lateral HEMT 100 constitutes acounterpart of a so-called body diode between body and drain of a knownMetal Oxide Semiconductor Field Effect Transistor (MOSFET), e.g., a SiMOSFET. Thus, the rectifying junction improves the operability of thelateral HEMT when switching inductive loads, for example. Furtherbenefits of the lateral HEMT 100 include an improved robustness at highvoltages during operation such as in avalanche mode, discharge of highcurrents to source and avoidance of discharge to a gate or to gatedriver circuits, and avoidance of a voltage shift of a threshold voltageV_(th) by charge trapping at the gate.

FIG. 2 illustrates a diagrammatic plan view of a section of the lateralHEMT 100 illustrated in FIG. 1. Components of the same function as thosein FIG. 1 are identified by the same reference numbers and are notexplained again below. The cross-section illustrated in FIG. 1 is takenalong the line A-A′ illustrated in FIG. 2.

The gate electrode 118 of the lateral HEMT 100 is arranged in avertically lower layer which cannot be seen in the top view of FIG. 2,and is therefore illustrated by a dashed line. Likewise, the Schottkycontact metal 132 is arranged in a vertically lower layer which cannotbe seen in the top view of FIG. 2, and is therefore illustrated byanother dashed line. Similarly, the through contact 119 is arranged in avertically lower layer which cannot be seen in the top view of FIG. 2,and is therefore illustrated by yet another dashed line.

In the embodiment illustrated in FIG. 2, the source electrode 116, thedrain electrode 117, the gate electrode 118 and the rectifying junctionare shaped as stripes extending parallel to each other. The drift region114 extends between the source electrode 116 and the drain electrode117. The Schottky contact metal 132 is electrically coupled to thesource electrode 116 via the through contact 119 and the wiring 115.

The shortest lateral distance d₁ between the gate electrode 118 and thedrain electrode 117 is larger than the shortest lateral distance d₂between the rectifying junction and the drain electrode 117, i.e., arelation d₁>d₂ holds.

In other embodiments, the source electrode 116, the drain electrode 117,the gate electrode 118 and the rectifying junction or at least part ofthese elements are shaped different from a stripe. By way of example,ring shape and/or polygonal shape may also be applied.

FIG. 3A illustrates a diagrammatic cross-section through a section of alateral HEMT 200 according to another embodiment. Similar to the lateralHEMT 100 illustrated in FIG. 1, the lateral HEMT 200 includes asubstrate 222, a buffer layer 221, a first semiconductor layer 211, asecond semiconductor layer 212, a two-dimensional electron gasschematically illustrated by a dashed line 224, a source electrode 216,a drain electrode 217, a gate electrode 218, a rectifying junction inthe form of a Schottky junction illustrated by a dashed line 231, aSchottky contact metal 232, a passivation layer 213 and a drift region214 between the source electrode 216 and the drain electrode 217.

The diagrammatic cross-section of the embodiment illustrated in FIG. 3Afurther includes at least one field plate 237. The at least one fieldplate 237 is arranged at least partially on the passivation layer 213 ina region of the drift region 214. The at least one field plate 237includes an electrically conductive material such as a metal or highlydoped polysilicon. By way of example, the at least one field plate 237may be a part of a patterned metal layer or metal alloy layer such as alayer or layer stack including Al, AlSi, AlTi, AlCu, AlSiTi, AlSiCu, Cu.In the illustrated embodiment, the at least one field plate 237 iselectrically coupled to the gate electrode 218 via a through contact219′. The through contact 219′ is arranged between the at least onefield plate 237 and the gate electrode 218 in a region of thepassivation layer 213 and directly contacts both the at least one fieldplate 237 and the gate electrode 218. The through contact 219′ includesan electrically conductive material, for example a metal or highly dopedpolysilicon.

In the embodiment illustrated in FIG. 3A, a shortest lateral distance d₂between the Schottky contact metal 232 of the rectifying junction andthe drain electrode 217 is larger than a shortest lateral distance d₃between the at least one field plate 237 and the drain electrode 217,i.e., a relation d₂>d₃ holds.

As illustrated schematically in FIG. 3A, when the lateral HEMT 200 isreverse-biased, a region 235 in which breakdown occurs may be pinnedtoward the ends of the field plates 237 which are laterally closer tothe drain electrode 217. The two-dimensional electron gas isdeteriorated locally in these regions 235 of the drift region 214 by hotcarriers. However, in the remaining regions of the drift region 214, theelectric field strength may be sufficiently lowered to avoid breakdownin these regions and thus to avoid a deterioration of thetwo-dimensional electron gas in these regions. Thus, when the lateralHEMT 200 is in a conductive mode, the two-dimensional electron gas andhence a conductive channel may be provided in a large area of the driftregion 214.

FIG. 3B illustrates another diagrammatic cross-section through a sectionof the lateral HEMT 200. The cross-section the lateral HEMT 200illustrated in FIG. 3B is similar to the cross-section the lateral HEMT100 illustrated in FIG. 1. Thus, reference is drawn to the descriptionrelated to FIG. 1. A pattern of a wiring 215 electrically coupling theSchottky contact metal 232 to the source electrode 216 may correspond tofingers of a comb-shaped structure including the source electrode 216and the plurality of fingers.

FIG. 4 illustrates a diagrammatic plan view of a section of the lateralHEMT 200 illustrated in FIGS. 3A and 3B. Components of the same functionas those in FIGS. 3A and 3B are identified by the same reference numbersand are not explained again below. The cross-section illustrated in FIG.3A is taken along the line B-B′ illustrated in FIG. 4 and thecross-section in FIG. 3B is taken along the line A-A′ illustrated inFIG. 4.

The gate electrode 218 of the lateral HEMT 200 is arranged in avertically lower layer which cannot be seen in the top view of FIG. 4,and is therefore illustrated by a dashed line. Likewise, the Schottkycontact metal 232 is arranged in a vertically lower layer which cannotbe seen in the top view of FIG. 4, and is therefore illustrated byanother dashed line. Similarly, the through contacts 219, 219′ arearranged in a vertically lower layer which cannot be seen in the topview of FIG. 4, and are therefore illustrated by yet another dashedline, respectively.

In the embodiment illustrated in FIG. 4, the source electrode 216, thedrain electrode 217, the gate electrode 218 and the rectifying junctionare shaped as stripes extending parallel to each other. The drift region214 extends between the source electrode 216 and the drain electrode217.

In the illustrated embodiment, a lateral distance between neighboringfield plates 237, 237′ is denoted by d₄. In a non-illustratedembodiment, more than two field plates are present. The distance betweentwo neighboring field plates may be the same for all the field plates.In another non-illustrated embodiment, a first plurality of field platesincludes a first lateral distance between neighboring field plates and asecond lateral distance between neighboring field plates, the firstlateral distance being different from the second lateral distance. Infurther non-illustrated embodiments, some or all lateral distancesbetween neighboring field plates are different from one another.

In the illustrated embodiment, the lateral distance d₃ between a firstone of the field plates 237 and the drain electrode 217 equals thelateral distance d₃ between a neighbor one the field plates 237′ and thedrain electrode 217. In a non-illustrated embodiment, these distancesmay be different from one another.

In the illustrated embodiment, a relation d₂>d₃ applies. According toother embodiments, d₂ may equal d₃ or a relation d₂<d₃ may apply.

In the embodiment illustrated in FIG. 4, a lateral width of the firstfield plate 237 denoted by w_(f1) equals the lateral width of theneighbor field plate 237′ denoted by w_(f2). In other embodiments thewidths w_(f1) and w_(f2) may differ from each other. Each of the fieldplates 237, 237′ has a lateral width smaller than a lateral width w_(d)of the drift region 214, i.e., w_(f1)<w_(d) and w_(f2)<w_(d).

In the embodiment illustrated in FIG. 4, the field plates 237, 237′ areelectrically coupled to the gate electrode 218. According to otherembodiments, different field plates may be electrically coupled to oneor different ones of the source electrode 216, the gate electrode 218,the drain electrode 217, a voltage different from the voltage of any ofthe source electrode 216, the gate electrode 218, the drain electrode217. By way of example, all of the field plates may be electricallycoupled to the drain electrode 217. According to another example, all ofthe field plates may be electrically coupled to the source electrode216. According to yet another example, a first one or a first pluralityof field plates is electrically coupled to the source electrode 216 anda second one or a second plurality of field plates is electricallycoupled to the drain electrode 217.

In the embodiments illustrated in FIGS. 1 to 4, the first semiconductorlayer 111, 211 includes GaN and the second semiconductor layer 112, 212includes AlGaN and the two-dimensional electron gas is located at theinterface between the first semiconductor layer 111, 211 and the secondsemiconductor layer 112, 212 toward the first semiconductor layer 111,211, which is also called Ga-face polarity. The HEMT is then also called“normal HEMT”. In non-illustrated embodiments, the first semiconductorlayer 111, 211 includes AlGaN and the second semiconductor layer 112,212 includes GaN. The two-dimensional electron gas is thus located atthe interface between the first semiconductor layer 111, 211 and thesecond semiconductor layer 112, 212 toward the second layer, which isalso called N-face polarity. The lateral HEMT is then also called“inverted HEMT”.

In further non-illustrated embodiments, both the first semiconductorlayer 111, 211 and the second semiconductor layer 112, 212 are undopedand the two-dimensional electron gas at the interface between the firstsemiconductor layer 111, 211 and the second semiconductor 112, 212 layeris formed due to the piezoelectric effect. The HEMT is then also called“PI-HEMT” (Polarization Induced High Electron Mobility Transistor).

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. A lateral HEMT, comprising: a first semiconductorlayer on a second semiconductor layer; a heterojunction at an interfacebetween the first semiconductor layer and the second semiconductorlayer; and a rectifying Schottky junction having a first terminalelectrically coupled to a source electrode and a second terminalelectrically coupled to the second semiconductor layer.
 2. The lateralHEMT of claim 1, wherein the second semiconductor layer is at least partof the second terminal.
 3. The lateral HEMT of claim 1, wherein thesecond terminal includes the second semiconductor layer and the firstterminal includes a Schottky contact metal of at least one of Ni, Pt, W,Mo, TiSi₂, WSi₂, and CoSi₂ on the second semiconductor layer.
 4. Thelateral HEMT of claim 1, wherein a gate electrode of the lateral HEMTand a Schottky contact metal of the Schottky junction are separate partsof the same patterned metal layer.
 5. The lateral HEMT of claim 1,wherein the rectifying Schottky junction includes at least one of p-typeGaN and doped polysilicon.
 6. The lateral HEMT of claim 1, wherein ashortest lateral distance between a gate electrode of the lateral HEMTand a drain electrode of the lateral HEMT is larger than the shortestlateral distance between the rectifying Schottky junction and the drainelectrode.
 7. The lateral HEMT of claim 1, wherein the firstsemiconductor layer comprises AlGaN and the second semiconductor layercomprises GaN.
 8. The lateral HEMT of claim 1, wherein the firstsemiconductor layer comprises GaN and the second semiconductor layercomprises AlGaN.
 9. The lateral HEMT of claim 1, wherein the sourceelectrode, a drain electrode of the lateral HEMT, a gate electrode ofthe lateral HEMT, and the rectifying junction are generally shaped asstripes extending parallel to each other.
 10. The lateral HEMT of claim1, further comprising: a passivation layer above the secondsemiconductor layer; a drift region having a lateral width w_(d); and atleast one field plate arranged at least partially on the passivationlayer in a region of the drift region and having a lateral width w_(f),wherein w_(f)<w_(d).
 11. The lateral HEMT of claim 10, wherein the atleast one field plate is electrically coupled to one of the sourceelectrode, a drain electrode of the lateral HEMT, a gate electrode ofthe lateral HEMT, and another electrode.
 12. The lateral HEMT of claim1, further comprising a substrate made of Si, SiC, GaN or Al₂O₃ and atleast one buffer on the substrate.
 13. The lateral HEMT of claim 1,further comprising a metal carrier substrate.
 14. The lateral HEMT ofclaim 1, further comprising a gate electrode arranged on the secondsemiconductor layer.
 15. The lateral HEMT of claim 1, further comprisinga recessed gate electrode partially extending into the secondsemiconductor layer.
 16. The lateral HEMT of claim 1, wherein the firstterminal of the rectifying Schottky junction is electrically coupled tothe source electrode via a plurality of interconnection fingers whichform part of a comb-shaped structure including the source electrode andthe plurality of interconnection fingers.
 17. A lateral HEMT,comprising: a first semiconductor layer on a second semiconductor layer;a heterojunction at an interface between the first semiconductor layerand the second semiconductor layer; a Schottky junction including aSchottky contact metal on the second semiconductor layer, the Schottkycontact metal being electrically coupled to a source electrode; andwherein a shortest lateral distance between a gate electrode and a drainelectrode is larger than the shortest lateral distance between theSchottky junction and the drain electrode.
 18. The lateral HEMT of claim17, further comprising: a passivation layer above the secondsemiconductor layer; a drift region having a lateral width w_(d); and atleast one field plate arranged at least partially on the passivationlayer in a region of the drift region and having a lateral width w_(f),wherein w_(f)<w_(d).
 19. The lateral HEMT of claim 17, wherein the gateelectrode is arranged on the second semiconductor layer.
 20. The lateralHEMT of claim 17, wherein the gate electrode is a recessed gateelectrode extending partially into the second semiconductor layer. 21.The lateral HEMT of claim 17, wherein a first terminal of the rectifyingSchottky junction is electrically coupled to the source electrode via aplurality of interconnection fingers which form part of a comb-shapedstructure including the source electrode and the plurality ofinterconnection fingers.
 22. A lateral HEMT, comprising: a firstsemiconductor layer on a second semiconductor layer; a heterojunction atan interface between the first semiconductor layer and the secondsemiconductor layer; a rectifying Schottky junction having a firstterminal electrically coupled to a source electrode and a secondterminal electrically coupled to the second semiconductor layer; apassivation layer above the second semiconductor layer; a drift regionhaving a lateral width w_(d); and at least one field plate arranged atleast partially on the passivation layer in a region of the drift regionand having a lateral width w_(f), wherein w_(f)<w_(d).
 23. The lateralHEMT of claim 22, further comprising a gate electrode arranged on thesecond semiconductor layer.
 24. The lateral HEMT of claim 22, furthercomprising a recessed gate electrode partially extending into the secondsemiconductor layer.
 25. The lateral HEMT of claim 22, wherein the firstterminal of the rectifying Schottky junction is electrically coupled tothe source electrode via a plurality of interconnection fingers whichform part of a comb-shaped structure including the source electrode andthe plurality of interconnection fingers.